Increasing rate of anti-SARS-CoV-2 antibodies between the first and second waves of COVID-19 in São Paulo, Brazil: A cross-sectional blood donors-based study.

BACKGROUND: SARS-CoV-2 infections rapidly spread along with Brazilian territory with heterogeneous transmission and mortality rates, mostly depending on region and period. Investigation of SARS-CoV-2 antibodies is an important tool to understand virus circulation. Given that blood donors are a representative casuistic of a healthy population, the authors evaluated the seroprevalence of IgG and IgM COVID-19 antibodies in 2,806 blood donors from a blood bank located in São Paulo, Brazil. METHODS: Aiming to evaluate viral behavior over time, the authors selected samples from blood donors who donated in June and October 2020, and February 2021. To determine whether socio-demographic features affected the seroprevalence, the authors analyzed samples from three different regions from São Paulo (capital, metropolitan and countryside regions) and evaluated predictors as gender, age, educational level, race, and use of public transportation. RESULTS: As expected, the authors observed that seroprevalence increased over time. Seroprevalence was greater in São Paulo city compared to metropolitan and countryside regions, being smallest in the countryside. Characteristics associated with a lower percentage of antibodies were age above 50 years, higher educational level, self-declared Caucasian, and use of individual transportation. CONCLUSION: In conclusion, blood donors' samples proved to accurately reflect virus circulation in the healthy population.

Characterization of RHD alleles present in serologically RHD-negative donors determined by a sensitive microplate technique.

BACKGROUND AND OBJECTIVES: Weak D phenotypes with very low antigen densities and DEL phenotype may not be detected in RhD typing routine and could be typed as D-negative, leading to D alloimmunization of D-negative recipients. The present study aimed to investigate the presence of RHD-positive genotypes in blood donors typed as D-negative by an automated system using the solid-phase methodology as a confirmatory test. METHODS: Two screenings were performed in different selected donor populations. For the first screening, we selected 1403 blood donor samples typed as D-negative regardless of the CE status, and in the second screening, we selected 517 donor samples typed as D-negative C+ and/or E+. RhD typing was performed by microplate in an automated equipment (Neo-Immucor®), and the confirmatory test was performed by solid-phase technique using Capture R® technology. A multiplex PCR specific to RHD and RHDψ was performed in a pool of 6 DNA samples. Sequencing of RHD exons was performed in all RHD-positive samples, and a specific PCR was used to identify the D-CE(4-7)-D hybrid gene. RESULTS AND CONCLUSION: No weak D type was found in either screening populations. Additionally, 353 (18·4%) D-negative samples presented previously reported non-functional RHD genes, 2 samples had a DEL allele, and 6 samples demonstrated new alleles, including one novel DEL allele. Our study identified six new RHD alleles and showed that the inclusion of a confirmatory test using serological methodology with high sensitivity can reduce the frequency of weak D samples typed as D-negative.